The One Laptop Per Child project is about to find out whether Microsoft is the solution to its problems in spreading inexpensive portable computers to schoolchildren. Microsoft and the laptop organization announced Thursday that the nonprofit's green-and-white "XO" computers now can run Windows in addition to their homegrown interface, which is built on the open Linux operating system.

Nicholas Negroponte, the founder of the laptop project - which aims to produce $100 computers but now sells them at $188 - acknowledged that having Windows as an option could reassure education ministers who have hesitated to buy XOs with its new interface, called Sugar. Sugar was designed only to work with a free Linux operating system that engineers from Red Hat. Eventually, the goal will be to develop versions of the laptop to run both Linux and Windows, leaving the user to decide which operating system to run when the machine boots up, Negroponte said.

Negroponte had hoped to sell several million laptops by now; instead he has gotten about 600,000 orders.

Beginning in limited runs next month, XO buyers will have the option of computers loaded with or without Windows. Versions with Windows will cost $18 to $20 more.

Not long after Negroponte first dreamed up the idea of seeding the developing world with $100 laptops for education, he talked with Microsoft about using a version of Windows on the machines. That seemed to vanish before long, as Microsoft's Bill Gates and a close partner, Intel Chairman Craig Barrett, publicly dismissed the XOs' scaled-back processing power and small screen.